Probably my Wii. Owned it a good 15 months but only VERY rarely used it.
(I'm not counting some of the retro stuff I got off eBay which is just sitting in boxed waiting to be sold because I can't/won't use them)
One of my mates bought it, didn't really have any use for it as he was just in the mood for blowing some cash he had made during the summer. Only played on it a couple times for a max of 20 minutes at a time (Wii Sports), so it really was good as new.
It sat in a cupboard for about a year, I then ended up picking up Super Mario Galaxy. Played through that and thoroughly enjoyed it, then got Brawl and played that for a bit, wasn't too impressed with the Super Smash Bros. series to begin with, so this wasn't really the best thing since sliced bread to me, as it was to many other gamers. Never was that big on Ninty anyway to tell you the truth, although I did mostly own Nintendo consoles back in the day (GB, NES and SNES were all brilliant, don't get me wrong).
After sussing out that it wasn't ever going to get as good as Super Mario Galaxy I decided to sell it on after about 15 months of owning it, only finishing SMG and playing roughly 30 minutes total of Wii Sports and SSBB on it. I ended up slightly regretting it for a while after hearing about Super Mario Galaxy 2 and New Super Mario Bros. Wii, but we'll get 'round to playing those later I think.
I also bought a PS3 40 gb back when I lived/studied in China for a year, only played it in Shanghai at my mate's appartment for a few hours, then his brother took it home to Belgium where I absolutely NEVER touched it and just ended up going for the easy money and sold it. I did "own" it a bit longer than the Wii, so it gets an honorable mention as the system I had the least use for.
I'm planning on getting a 60 gb soon though, for Blu-ray mostly and I really want to get round to playing MGS4 after going through all previous MGS titles again.
Always on the look-out for fighting games!
Have any stray ones laying about? Let me know and we'll try to give them a cosy new home.